Wafer transport systems configured for use in semiconductor wafer-level processing typically include a stage having a chuck that secures the wafer for processing. Sometimes the stage is stationary, and sometimes it is moveable. Some applications require that the stage move linearly in one, two, or three Cartesian dimensions, with or without rotation. The speed of the stage motion can dictate the throughput of the entire wafer processing platform if a significant amount of the total process time is spent aligning and transporting the wafer.
Some systems have the flexibility to move the processing and inspection devices to the wafer as well as move the wafer to the devices. This can eliminate wafer alignment steps and thereby save time. For applications including laser processing, a moveable optics assembly can be mounted above the wafer surface, thereby minimizing the wafer transport distances required. The chuck holding the wafer, or specimen, to be processed may be mounted to a major axis stage for movement in the primary direction of stage motion, a minor axis stage for movement in a direction perpendicular to the primary direction of stage motion, or in a stationary position below the major and minor axes. The major axis stage may support the minor axis stage, or they may be independent of each other.
Stage design of such optical systems is becoming more critical as electrical circuit dimensions shrink. One stage design consideration is the impact of process quality stemming from vibrational and thermal stability of the wafer chuck and optics assembly. In the case in which the laser beam position is continually adjusted, state-of-the-art structures supporting the laser assembly are too flexible to maintain the required level of precision. Moreover, as circuit dimensions shrink, particle contamination becomes of greater concern.
In semiconductor wafer fabrication, many wafer processing operations are followed by an inspection to ensure that an operation was successful before moving a wafer on to a next processing step. The inspection may be conducted with use of a separate piece of equipment, usually a powerful optical microscope or an electron microscope. Or, the inspection equipment may be directly built into a processing system platform, eliminating overhead associated with delivery of wafers to an additional station. Transporting a heavy processing or inspection device unnecessarily is also undesirable, because the accuracy and stability of a moving structure is optimized when its mass is low. In addition, thermal dissipation increases with motor size and, therefore, with payload mass.